Causes of Hair Loss

Most people normally shed 50 to 100 hairs a day. This usually doesn’t cause noticeable thinning of scalp hair because new hair is growing in at the same time. Hair loss occurs when this cycle of hair growth and shedding is disrupted or when the hair follicle is destroyed and replaced with scar tissue.
The exact cause of hair loss may not be fully understood, but it’s usually related to one or more of the following factors:
Family history (heredity)
Hormonal changes
Medical conditions
Medications

Other causes of hair loss
Hair loss can also result from:
Radiation therapy to the head. The hair may not grow back the same as it was before.
A trigger event. Many people experience a general thinning of hair several months after a physical or emotional shock. This type of hair loss is temporary. Examples of trigger events include sudden or excessive weight loss, a high fever, surgery, or a death in the family.
Certain hairstyles and treatments. Excessive hairstyling or hairstyles that pull your hair tight, such as pigtails or cornrows, can cause traction alopecia. Hot oil hair treatments and permanents can cause inflammation of hair follicles that leads to hair loss. If scarring occurs, hair loss could be permanent.